1. Field of the Invention
This invention relates in general to subsea well equipment, and in particular to a riser extending from a subsea well system to a floating production vessel at the surface.
2. Description of the Prior Art
In deep water subsea well systems, often a number of wells will be drilled through a subsea template, then completed. These wells may be connected to a production riser that extends normally to a floating production vessel at the surface. Well fluids flow up the production riser to the production vessel, where the fluids are treated to remove water and separate gas. The well fluids often then are pumped back down to the template and to a pipeline located on the sea floor which extends to a gathering station at a remote area.
The buoyant riser comprises sections of a central conduit which have flanges on their ends for bolting together to form a continuous riser string. Smaller diameter conduits are connected in sections and bolted around the central conduit. The smaller conduits convey production fluids from the template to the surface, with the larger central pipe being used to convey the treated well fluids back down to the subsea wells. Hydraulic pressure is also supplied through some of the smaller conduits for controlling the wells.
An air can surrounds the assembled conduits, and for each section extends downwardly to a point near the lower flange. Air is injected into the air can to displace some of the water in the air can to provide buoyancy and reduce the weight of the riser string. The structural load is carried entirely by the central conduit. The installation of such a riser system is very time consuming and expensive because of the numerous connections that must be made with each section.